1. Field of the Invention
The present invention relates to an automotive alternator and an automotive alternator brush abrasion detection system mounted to an automobile, etc.
2. Description of the Related Art
FIG. 23 is a longitudinal section showing a conventional automotive alternator, FIG. 24 is a perspective of a rear bracket interior portion of the conventional automotive alternator viewed from a front end, FIG. 25 is a perspective showing a brush holding apparatus used in the conventional automotive alternator, FIG. 26 is a perspective showing a rotor used in the conventional automotive alternator, and FIG. 27 is an electrical circuit diagram for an automotive vehicle mounted with the conventional automotive alternator.
In FIGS. 23 to 27, an automotive alternator 100 is constructed by rotatably mounting a Lundell-type rotor 7 by means of a shaft 6 inside a case 3 constituted by a front bracket 1 and a rear bracket 2 made of aluminum and fixing a stator 8 to an inner wall surface of the case 3 so as to cover an outer circumferential side of the rotor 7.
The shaft 6 is rotatably supported in the front bracket 1 and the rear bracket 2. A pulley 4 is fixed to a first end of this shaft 6, enabling rotational torque from an engine to be transmitted to the shaft 6 by means of a belt (not shown). A pair of slip rings 9 functioning as electric current supplying members for supplying an electric current to the rotor 7 are disposed on a second end portion of the shaft 6 so as to be separated in an axial direction and be able to rotate together with the shaft 6.
The rotor 7 is constituted by: a rotor coil 13 for generating a magnetic flux on passage of an electric current; and first and second pole cores 20 and 21 disposed so as to cover the rotor coil 13, magnetic poles being formed in the first and second pole cores 20 and 21 by the magnetic flux generated by the rotor coil 13. The first pole core 20 is made of iron, first claw-shaped magnetic poles 22 having a tapered shape being formed at a uniform angular pitch in a circumferential direction on an outer circumferential edge portion of the first pole core 20 such that the direction of taper of each of the first claw-shaped magnetic poles 22 is aligned with an axial direction. The second pole core 21 is made of iron, second claw-shaped magnetic poles 23 having a tapered shape being formed at a uniform angular pitch in a circumferential direction on an outer circumferential edge portion of the second pole core 21 such that the direction of taper of each of the second claw-shaped magnetic poles 23 is aligned with an axial direction. The first and second pole cores 20 and 21 are fixed to the shaft 6 facing each other such that the first and second claw-shaped magnetic poles 22 and 23 intermesh with each other. In addition, fans 5 are fixed to end surfaces of the first and second pole cores 20 and 21, respectively. The pair of slip rings 9 are electrically connected in series through the rotor coil 13.
The stator 8 is provided with: a cylindrical stator core 15 in which slots are disposed at a predetermined pitch in a circumferential direction; and a three-phase stator winding 16 installed in the stator core 15.
A rectifier 12 for converting alternating current generated in the stator 8 into direct current is mounted inside the case 3, the rectifier 12 being constituted by a three-phase full-wave rectifier in which three diode pairs are connected in parallel, each diode pair being composed of a positive-side diode d1 and a negative-side diode d2 connected in series.
A brush holding apparatus 29 is provided with a body 30 in which a brush holder portion 31, an annular shaft insertion portion 32, a circuit housing portion 33, a connector portion 34, etc., are molded integrally using an electrically-insulating resin. A conductor group is insert molded into the body 30. The conductor group constitutes wiring among the elements mounted to the body 30, projects inside the connector portion 34 to constitute external connection terminals, and exposes in required portions to constitute rectifier connection terminals 35 functioning as an electrical connection portion for connection to the rectifier 12.
Brush insertion apertures (not shown) perpendicular to a central axis of the shaft insertion portion 32 are formed in the brush holder portion 31 so as to communicate between the shaft insertion portion 32 and an external portion, a cap 31a being removably mounted to a head portion of the brush holder portion 31 so as to cover an opening at an opposite end of the brush insertion apertures from the shaft insertion portion 32. A pair of brushes 10 are housed in the brush insertion apertures of the brush holder portion 31, being forced toward the shaft insertion portion 32 by springs 11. Lead wires 14 are connected to head portions of each of the brushes 10.
A voltage regulator 18 for adjusting the magnitude of an alternating voltage generated in the stator 8 is fixed to a heat sink 17. The heat sink 17 is mounted by being fitted into the circuit housing portion 33, the voltage regulator 18 being housed inside the circuit housing portion 33.
The brush holding apparatus 29 is securely fastened to an inner wall surface of the rear bracket 2 such that the center of the shaft insertion portion 32 is aligned with a central axis of the rear bracket 2. The shaft 6 is inserted inside the shaft insertion portion 32, the pair of brushes 10 being placed in contact with the pair of slip rings 9 by the force of the springs 11. Thus, the brushes 10 slide on the slip rings 9 with the rotation of the shaft 6.
In the conventional automotive alternator 100 constructed in this manner, an electric current is supplied to the rotor coil 13 from a battery 27 constituting a power supply through the brushes 10 and the slip rings 9, generating a magnetic flux. The first claw-shaped magnetic poles 22 of the first pole core 20 are magnetized into North-seeking (N) poles by this magnetic flux, and the second claw-shaped magnetic poles 23 of the second pole core 21 are magnetized into South-seeking (S) poles. At the same time, rotational torque from the engine is transmitted to the shaft 6 by means of the belt (not shown) and the pulley 4, rotating the field rotor 7. Thus, a rotating magnetic field is imparted to the stator winding 16, generating an electromotive force in the stator winding 16. This alternating-current electromotive force passes through the rectifier 12 and is converted into direct current, the magnitude thereof is adjusted by the regulator 18, the battery is charged, and the current is supplied to an electrical load 28.
After commencement of power generation, the alternator 100 is switched to “self-excitation” by supplying a portion of the output current from the alternator 100 to the rotor coil 13 through the brushes 10.
In this conventional automotive alternator 100, because the brushes 10 are pressed against the slip rings 9 by the springs 11, they are abraded with the rotation of the shaft 6. Excessive abrasion of the brushes 10 in this manner gives rise to defective power generation, causing the internal combustion engine to stop due to insufficient electric power from the electrical system, leading to a breakdown of the automotive vehicle. Because the conventional automotive alternator 100 does not have a means for detecting abrasion of the brushes 10, one problem has been that the brushes 10 may be abraded excessively, leading to a breakdown of the automotive vehicle without the driver of the vehicle being warned in advance.
Furthermore, when power generation becomes defective in the conventional automotive alternator 100, if the automotive electrical circuit is continuously open, the battery 27 is discharged. It is possible to restart the internal combustion engine by recharging the battery 27, but once the battery 27 has been discharged, its service life deteriorates significantly, and so another problem has been that the battery 27 has had to be changed.
Brush abrasion detecting apparatuses for dynamoelectric machines, have been proposed, for example, in Japanese Utility Model No. 3020646, Japanese Utility Model No. 3020647, Japanese Patent Examined Publication No. HEI 3-15413, Japanese Patent No. 2922266, Japanese Patent Examined Publication No. SHO 57-38841, etc.
However, even if these brush abrasion detecting apparatuses are adopted in this conventional automotive alternator 100 to enable the driver of the vehicle to be informed in advance of excessive abrasion of the brushes 10, because the brush holding apparatus 29 is housed inside an airtight case 3, brush replacement is difficult, and one problem has been that time is required before recommencing operation of the vehicle.
More specifically, when the brushes 10 become abraded, first the automotive alternator 100 is removed from the internal combustion engine and taken out of the vehicle, and the brush holding apparatus 29 is extracted by dismantling the automotive alternator 100. Then the cap 31a is removed, the operation of replacing the brushes 10 is performed, the cap 31a is mounted, then the brush holding apparatus 29 is mounted to the rear bracket 2 and the automotive alternator is reassembled. Next, the automotive alternator 100 is mounted to the internal combustion engine. Thus, the brush replacement operation is extremely complicated and requires a great number of man-hours.
In recent years, reductions in internal combustion engine space have been sought with a view to ensuring maximum passenger compartment space within the framework of vehicle codes, and there is a tendency for auxiliary devices such as air discharge pipes, water pumps, etc., to be clustered close together around the automotive alternator 100, reducing the space available for the removal and replacement of the automotive alternator 100. Thus, another problem has been that removal and replacement of the automotive alternator 100 is becoming even more difficult, preventing the brushes from being replaced simply.